The present invention relates to flowmetering equipment and, in particular, to a flowmeter utilizing an asymmetric center body and a laminar proportional amplifier.
Numerous arrangements have been proposed by those skilled in the art which exploit the phenomenon of the Karman vortex street in order to measure fluid flowrates. More than a decade ago W. G. Bird devised an arrangement in which a pivoted vane-like element was positioned downstream of a vortex shedding body. Flowrate was measured by detecting the frequency of pivotal oscillation of the element. Later, A. E. Rodely recognized that a suitable dimensioned bluff body, having a base surface facing fluid flow and downstream surfaces to control oscillatory flow, would produce vortex shedding free of intermittency. In this arrangement, a temperature sensitive sensor situated outside the wake generated by the bluff body detects vortex shedding and produces electrical pulses proportional to the flow rate. The sensor is mounted separately in the pipeline wall and the probe-like sensor is positioned in the low turbulence flow zone outside of the wake.
Improved versions of the Rodely bluff body flowmeter generally detect vortex shedding in the high turbulence flow zone immediately downstream of the base surface of the bluff body. While these arrangements represent significant contributions to the state of the art, none has generally been suitable for measuring the flowrate of fluids at very low and very high Reynolds numbers. The frequency with which vortices are shed in a Karman vortex street behind a blunt body is dependent on the flow velocity, which is, in turn, a function of the Reynolds number R of the fluid, which is given by the equation: EQU R=.rho.VD/.mu.
where D=the cross-sectional width of the blunt body, V=the velocity of the fluid, .rho.=the density of the fluid and .mu.=the viscosity of the fluid.
The best type of flowmeter would be one that would measure flow rates from very low to very high Reynolds numbers. In the past, this has been difficult to achieve. It has been observed that a regular Karman vortex street can be generated behind a blunt body only when the Reynolds number of the fluid is in the range of about 60 to 5,000. At Reynolds numbers below 60, the flow around the body is laminar and no vortices are formed; at Reynolds numbers above 5,000, there is complete turbulent mixing which completely covers the Karman street. Most flowmeters are therefore designed to operate at Reynolds numbers between 500 and 5,000.